John,
Are you talking about b/w or color illustrations? If b/w, you could have them
run out on an imagesetter at 2450 dpi then enlarged photographically by any
photo lab that does prints of the size you need. Rather than running out a
positive, I'd check with the lab, find out if they can use 8×10 negatives, then
run out a negative for them in that size.
If color, you might get a color negative shot from your Illustrator file, say a
4×5, and have the photo lab enlarge that.
Steve
Read action !